The present disclosure relates generally to a ground fault protection circuit for a multi-source electrical distribution system, and particularly to a ground fault protection circuit for a multi-source electrical distribution system having multiple grounding points.
Electrical power distribution systems are often configured having a plurality of polyphase power sources, each including a plurality of phase conductors and a neutral conductor. In such a system, a polyphase main bus is connected to each one of the power sources and includes a plurality of phase conductors and a neutral conductor, with main circuit breakers electrically connected in respective ones of the main buses for interrupting power flowing therethrough. A polyphase tie bus is connected between each of the main buses and includes a plurality of phase conductors and a neutral conductor, with a tie circuit breaker electrically connected in the tie bus for interrupting power flowing therethrough. Each of the main and tie buses having phase and neutral current sensors for generating signals proportional to the currents in the associated phase and neutral conductors. In such power distribution systems, it is desirable to have a ground fault protection circuit to provide automatic circuit interruption of an appropriate section of the distribution system upon detection of an undesired ground fault condition. Existing techniques to provide for ground fault protection use a second set of phase and neutral current sensors for generating another set of signals proportional to the current in the associated phase and neutral conductors, with these additional signals then being used in a modified differential ground fault protection scheme. While such existing techniques are adequate for their intended purpose, such techniques require an additional set of four phase and neutral current sensors, resulting in a total of eight current sensors per circuit breaker (an original four used for relay and meter functions associated with the respective circuit breaker, and an additional four used for modified differential ground fault protection scheme).
As such, there remains a need in the art of ground fault protection in a multi-source electrical distribution system for a ground fault protection circuit that does not require so many current sensors per circuit breaker.